Various devices have been used in the past to heat a treatment region of an animal body for therapeutic purposes. In particular, it is known in the art to use a radio frequency (RF) or microwave electromagnetic field to induce hyperthermia in an animal body for the purpose of transforming or killing certain cells of the animal body. For example, focused microwave thermotherapy has been used for breast cancer treatment, in which a woman's breast is placed between two compression plates and a microwave unit positioned on each side of the breast applies an electromagnetic field across the breast. The amplitude of the electromagnetic field decreases as it penetrates further into the breast and, as such, the electromagnetic field is not constant throughout the thickness of the breast. Devices that utilize an electromagnetic field—whether operating at RF or microwave frequencies—do not evenly heat the entire thickness of a treatment region and, as a result, have not been able to achieve the desired therapeutic outcomes.